Sound insulation floor structures are applied to multi-storied (or multi-story) buildings (e.g., an apartment house or a condominium, a building, and a dwelling house) in order to reduce floor impact sounds from upstairs. The floor impact sounds include a light-weight impact sound (a relatively high-frequency sound wave) [such as an impact sound caused by dropping of tableware such as a spoon or an impact sound caused by walking with house shoes (or slippers)], an impact sound (a relatively low-frequency sound wave) [such as an impact sound caused by jumping of a child down from a sofa or an impact sound caused by noisily walking], and the like. The sound insulation floor structures are desirable to have wide-ranging impact sound insulation. It is known that the sound insulation floor structures are mainly obtainable by a method of pasting a buffer member on a wood board having a rear side provided with a plurality of kerfs (a method using what is called a direct pasted sound insulation floor member), a method of disposing a damping member (a sound insulation member) between a floor member and a floor backing member, or the like.
As a method using combination of a kerf and a buffer member, for example, Japanese Patent Application Laid-Open Publication No. 2004-44315 (JP-2004-44315A, Patent Document 1) discloses a soundproof floor member comprising a split board, a plywood base member having a plurality boards laminated and unified, and a groove section bored in the plywood base member; the split board is obtained by splitting a molding original sheet of a medium-density fiber board into the plural in a thickness direction thereof and has a hard layer on one side thereof; the hard layer lies in a front side of the soundproof floor member; and the split board is laminated and unified on a front side of the plywood base member. The plywood base member has the first outermost layer that is thinned in an approximately half of a normal layer lower than the first outermost layer, and the groove section is bored from a rear side of the plywood base member to the second outermost layer. When an impact is made on a floor, the soundproof floor member undergoes deformation of the wood board due to a plurality of kerfs provided on the rear side of the wood board. Since the deformed portion serves as a buffer to absorb the impact, the soundproof floor member shows an excellent effect on impact sources, in particular, a light-weight floor impact source. This document also discloses that the floor member has a strength enough to stand a load applied via casters in moving an object with casters on a floor by providing the hard portion comprising the medium-density fiber board on the front side of the plywood base member.
For the method using combination of the kerf and the buffer member, however, the wood board is locally deformed in a region loaded by walking (that is, the floor member subsides) even when the specific medium-density fiber board is disposed on the surface side. Thus there is an uncomfortable foot-step feeling during walking. Further, the floor has a small sound insulation effect on a heavy floor impact sound (for example, a relatively low-frequency sound wave), probably because the floor has a small space volume due to the insufficient size of the kerf.
As a method of interposing a damping member between a floor member and a floor backing member, for example, Japanese Patent No. 3013023 (JP-3013023B, Patent Document 2) discloses a sound insulation component for reducing a floor impact sound, in which a mixture containing 100 parts by weight of a petroleum-based asphalt, 2 to 10 parts by weight of a thermoplastic elastomer, 100 to 400 parts by weight of a mineral grain, 100 to 800 parts by weight of an iron powder, and 0.1 to 1 parts by weight of a surfactant is sandwiched between sheets, each consisting of a felt or a nonwoven fabric, and molded into a plate-like form.
The floor member provided with the damping member (the sound insulation component) is only slightly deformed due to walking and comfortable to walk, while the floor member has a lower ability to insulate a floor impact sound compared with the sound insulation floor member comprising combination of the kerf and the buffer member.
Incidentally, International Publication No. WO2007/116676 (Patent Document 3) discloses that a nonwoven fiber assembly containing a thermal adhesive fiber under moisture is heat-treated with a high-temperature water vapor to produce a hard shaped product having a nonwoven structure (or nonwoven fabric structure) and having the thermal adhesive fiber melt-bonded at a uniform bonded ratio in a thickness direction. This document discloses that the hard shaped product is available for a building board. This document is, however, silent on floor structures or sound insulation properties.